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waderoush writes "Forcing sulfur atoms into silicon using femtosecond laser pulses creates a material called 'black silicon' that is 100 to 500 times more sensitive to light than conventional silicon, in both the visible and infrared spectrums, according to SiOnyx, a venture-funded Massachusetts start-up that just emerged from stealth mode. Today's New York Times has a piece about the serendipitous discovery of black silicon inside the laboratory of Harvard physicist Eric Mazur. Meanwhile, a report in Xconomy explains how black silicon works and how SiOnyx and manufacturing partners hope to use it to build far more efficient photovoltaic cells and more sensitive detectors for medical imaging devices, surveillance satellites, and consumer digital cameras."

Just to be a bit more explicit, sensitivity probably refers to one of two things.

The first would be an increase in quantum efficiency; that would be an increase in the ratio of photons detected to those impacting. In a photovoltaic cell this would lead to improved efficiency. Current scientific detectors, that I've looked into anyway for a research project I'm involved in, max out at maybe 70%, with most reasonably priced ones being 25%-35%. (The 70% ones tend to be things like photomultiplier tubes which require power input to achieve a high reverse voltage, so they're certainly not useful for PV cells.)

The second aspect would be to decrease the noise or dark count so that its capable of detecting dimmer and dimmer light sources, and in order to get the > 100% improvements this is definitely a large aspect of what the new method has done. Unfortunately I know more about the applications and figures of merit than the semiconductor stuff, so I can't say much about this other than I hope this opens up some new application possibilities.

The efficiency of a solar cell is equal to the power absorbed by light divided by the power that is actually sent to the circuit the device is attached to.
So if the sensitivity of the collector increases 500x, then there is likely going to be a major increase in the power supplied by the cell. This has nothing to do with the efficiency

The sensitivity they are referring to is the amount of electrons released by the incident light - Amps of current per Watt of sunlight. Sunlight has a broad spectrum, and this technique allows more of the infrared portion of the spectrum (which is a lot) to cause electrons to flow.

However, and this is important, they achieved this by lowering the bandgap energy of the silicon. Why is that important? Remember that power, when it comes to electronics, is current times voltage. The voltage of a solar cell (open circuit voltage) is more or less the bandgap energy (divided by one electron charge). So, yeah, they get more electrons to flow for the same amount of incident sunlight, but the cell's voltage has also been lowered. Do you end up with more or less power as a result? Does the greater current overcome the lowered voltage? Since they haven't actually published data on a solar cell made from this technique, there isn't really a way to tell for certain.

My guess is that they won't be able to get vast power gains - possibly lower ones. The reason for this is that, right now, one photon with energy greater than the bandgap energy has a chance to create one electron-hole pair. If the photon has more energy than the bandgap energy, it doesn't make a correspondingly more energetic electron-hole pair. Even if the photon had twice the bandgap energy, it can't make two electron-hole pairs. So, a blue photon creates as much useful electrical energy as a red photon, despite the fact that the blue photon has more energy in it. One can play around with the bandgap energy of the PV cell to make better use of the high energy photons, but at the cost of excluding lower energy photons like infrared and red. More info here [google.com]. This is why the solar cells with greatest efficiency are actually multi-junction cells [wikipedia.org] - several solar cells with different bandgap energies stacked on top of each other, each tuned to a different portion of the solar spectrum.

The article mentions how these guys should be able to use their black silicon to create multiple electron-hole pairs from a single photon. In order to do that, however, they have to provide a bias voltage. In that case, the solar cell is sucking power, not producing it. That's fine if what you want is a very sensitive photo sensor - it's basically a solid-state photomultiplier tube. It's not a way to generate electrical power.

This is another company using the mystique of "Trade secrets" to attract capital. If this is as good as they say, they wouldn't have any secrets and would spill the beans.

I think they have found some weaknesses that restrict the usefulness of this technology. Perhaps sensors made with this technology must be supercooled in order for them to function properly (i.e. perhaps this technology amplifies thermal noise by dozens of times).

While I'm quite skeptical as well, you should keep in mind that patent applications sit in limbo for a few years before being approved. (And 'patent pending' does nothing.) If it's that good, it would make perfect sense to keep the details under wraps until the patent application is approved - at which point anyone can read about it, just not use it for a while.

You don't need to wait until a patent is granted to read it. US patent applications (for example) are published 18 months after they are filed, which is often years before they are granted (or not, as the case may be).

Yep, I agree. These days there's always a catch in everything. I guess that, even if some perfect tech came up, we'd find out the company's CEO was fucking the misses behind our back, or something like that.

If this is as good as they say, they wouldn't have any secrets and would spill the beans.

The fundamental research [harvard.edu] was done a long [latimes.com] time [physorg.com] ago [photonics.com](with picture of prototypes); I've read articles about it in Electronics and Wireless World several times over the years, so it's hardly a secret. Any potentially patentable critical element is going to be kept under wraps, obviously.

I think they have found some weaknesses that restrict the usefulness of this technology.

Or they spent 3 years on R&D fixing those weaknesses, like the article says.

Further information of note from the NYT article:

SiOnyx is already commercializing sensor-based chips as a technology development platform for other companies and for use in next-generation infrared imaging systems.

So we're told:1- There's a decade of peer-reviewed research behind the technology.2- They have funding and partners already.3- They're shipping parts now, not at some unknown time in the future.

Either this is real, or Dr Mazur et al are engaging in an exceptionally elaborate, very public and career-ending series of lies (and it's not as though SiOnyx will be a paying proposition if the tech doesn't work). The part of the operation that does look suspect is their web site [sionyxinc.com] (Flash warning), but that doesn't prove anything about the physics involved.

>...and it's not as though SiOnyx will be a paying proposition if the tech doesn't work...

It has already been a paying proposition for ten years for its employees, agents, consultants, lawyers, etc. This announcement could suck in enough new funding to stretch that another decade.

Note: I'm not saying that they don't have anything real: just that these things are often profitable for someone even when they don't pan out (and most don't). Look particularly at the venture capital types who get hefty fees

It has already been a paying proposition for ten years for its employees, agents, consultants, lawyers, etc.

SiOnyx was formed in 2005, not 1999. Before that the team had to get funding the same way as everyone else at Harvard: peer assessed grant applications, with results subject to review. That doesn't eliminate the possibility of it being a sham, but sustaining the illusion of success for that long in that environment would be an impressive feat.

I read through those articles and they don't say much about this technology at all.

That's true, the Xconomy article is the most technically informative available for free, you'll have to subscribe to one of the relevant journals to get anything more detailed. I added those to point out that this is not new, it already has funding, and they're at the stage of developing commercial fabrication processes. There is a clear, prefectly normal development history here, you being unaware of it doesn't mean it's a s

Please note they did not say it is 100 x more sensitive than all other detectors in the visible, just more sensitive than silicon, which itself is not sensitive in the visible without doping.

Small point: untreated silicon does not mean pure elemental silicon, it means it hasn't gone through this process. Obviously, if the type of silicon they're comparing this to has no sensitivity in the visible spectrum whatsoever they can't claim any relative improvement...100 times nothing is still nothing.

2. the power density of the beam (if they increase the spot size, the power density goes down, meaning it's more costly and difficult to expose larger portions of the wafer at once, hence increasing time and cost)

3. Sulfur Hexaflouride is apparently safe enough to inhale... well, as safe as helium, anyway. It will make your voice very deep, owing to its high density. There are countless Youtube videos that demonstrate all of the hijinx possible with this heavier-than-air gas.

However, since it displaces oxygen, you would eventually die from asphyxiation if you breathed it exclusively for several minutes.

If it's heavier than oxygen, wouldn't it pool at the bottom of your lungs? I.e. with each breath a little more SF6 gets left in your lungs, and pretty soon only the swept volume of your lungs is operational. It'd at least take more effort to clear SF6 from your system than He would.

CO2 is heavier than O2, and yet you aren't concerned about that, right?

This is pure speculation-- I fell asleep during Pulmonary Mechanics-- but I suspect the turbulence that arises from inhalation stirs up the unswept volume sufficiently that it gets replaced in short order.:)

I wouldn't say easy, but not too hard either: many years ago I remember visiting a school about optical where they had a 'tabletop' femtosecond laser.So it depends on the properties needed for the pulse: some femtosecond laser are tabletop materials, others are definitely more involved..

Not necessarily, the licensing office was completely mesmerized by bio-tech and drug patent licensing, this was neither and ignored until more enlightened personel were hired the office at Harvard.

Harvard, for its part, is holding up SiOnyx as one early result of the ongoing overhaul of the university's technology licensing efforts. The school gained a reputation early in this decade as being unresponsive, even hostile, toward faculty and students who wished to commercialize discoveries made in the university's labs, especially in areas outside of biotechnology and drug development. For years after the discovery of black silicon in Mazur's lab, the school's technology transfer office âoewasn't very excitedâ about the work, according to Carey.

... again. I love solar power, and I realize that it progresses in small increments. But there have been so many stories of "break through" improvements that I don't really care until a profoundly more efficient product is made. Black silicon have twice the sensitivity to light that regular silicon does, which is great news for digital cameras and night vision scopes. I might be great news for solar power, but tell me about it once you have a working prototype with a noteworthy efficiency improvement.

I might be great news for solar power, but tell me about it once you have a working prototype with a noteworthy efficiency improvement.

From what I've read this story is more about image sensors, but for solar cell applications: I don't understand the fuss about all these 'breakthrough efficiency record' stories. For all but a few applications (think satellites, pocket calculators etc.) efficiency doesn't matter. There is no shortage of sunlight, and therefore no need to turn a maximum of it into electricity. What matters is price per generated electric power ($/Watt), and how long the solar cells will last.

If I'm not mistaken, the solar cell market is hitting the 1 $/Watt mark around now, and growing at what, 10% ? 20% ? 50% per year? Wake me up when solar cells become cheaper than roof tiles, or provide a return on investment in <5 years (for average households), and will last decades after that. Then you have a breakthrough.

We are getting there. There are several companies that are currently making a large profit on Solar Cells. The basic science has all been performed. We know what material systems work the best (Silicon, CIGS, CdTe). There have been several improvements on production method of the last several years, as well. I personally believe ribbon silicon has the greatest promise. However, if researches can get solution deposited, nano-particle devices up to decent efficiencies, they could rule the market.

Efficiency counts in terms of size. Yes, if we need more power, we can build bigger collectors. However, in many cases space=money. Moreover, convenience=easier sell=more money.

There's already plenty of little solar gadgets for charging your cellular or whatever while camping, those wouldn't work too well if you needed an area the size of a football field to get enough power. More efficient collectors can mean (in general) that you can get *the same* amount of power (as a less efficient collector) in a smal

But there have been so many stories of "break through" improvements that I don't really care until a profoundly more efficient product is made.

Some years back, I read an article in an old magazine (I think it was a 1960's Popular Science) about a new method of blowing glass resulting in "near unbreakable" bottles. It went on excitedly for page, after page, talking about the new era of safety that this kind of glass could behest - glass that doesn't easily break - you could drop your soda or medicine bottle and it wouldn't shatter!

Intrigued, I spent an entire afternoon at the local University library trying to figure out exactly what happened to this miraculous technology! I even did some searching (AltaVista) on the then new-fangled Internet. The truth rather surprised me...

This "breakthrough" technology that had gone invisible was part of my everyday life, including the bottle of Diet Coke I was then slurping from! It had become so common that virtually nobody produced the old-fashioned fragile bottles and glass anymore!

That's why it works to have coffee tables with glass counter tops. That's why restaurants can get away with the sterile, easily cleaned, hard-to-scratch glass overlays on their tables. Next time you are at a corner market and see the glass countertop with the items for sale inside, think about that article in the ancient Popular Science article.

Once breakthroughs actually become available, they don't seem like breakthroughs - they quickly just become part of the landscape, and people don't notice them, anymore. This is why the "Intelligent Design" idiots can get out of their incredibly complex, affordable, high-tech SUVs and then announce that Science has it all wrong. Once it's routine, it no longer seems like such a big deal.

Proof? Affordable, thin-film photovoltaics is still largely considered a "breakthrough" technology. But there's a company doing it now, today, affordably [nanosolar.com]. Alas, while they are growing as fast as they are able, all their production capacity is already sold to germany. I'd suggest you read up on it [wikipedia.org].

High tech is introduced slowly. At first, the high engineering cost can only be paid in niche markets where the return on investment is fat. But as the original engineering cost gets paid back, and as the technology itself is matured and tested, the cost of implementation drops rapidly, so that it applies to more and more and more niches. By the time it's available for common Joes like you and me, it doesn't seem like such a big deal, and we are left wondering "where are the breakthroughs?" from our satellite/GPS navigated, MP3 playing, fuel-injected, ABS-brakes protecting, vulcanized rubber-tired, air-conditioned, hybrid gas/electric, high-tech wonder machine.

Where are the breakthroughs? Look at the beer bottle in your trashcan.

Very good point, but the attack on Intelligent Design doesn't _quite follow (sadly!).

Not that I am a fan of ID. Not on the same page at all. Perhaps not even in the same library. But there is nothing illogical about considering organisms to be 'designed' the same way that technology is.

I think it is because complex design is so familiar to us that it is easy for some people to assume that's how biological systems came about.

In fact, biological structures are very different to most human-designed artif

Wouldn't an ID advocate say that the trigger is a statistical nightmare to have been constructed by random clumping in a presumably adverse environment? I understood that the argument was: at a certain amount of complexity was required for a 'device' to have existed in the first place. That while random chance can produce interesting groupings or patterns etc, physical demands actually makes it impossible to the parts to have 'self-assembled' because physics actually prevents all parts from occurring origin

You are right, that is the idea. From Behe's book "Darwin's Black Box" (a pretty stupid book) the 'problem' is that systems can be "irreducibly complex". That is, like the mousetrap - remove or change any part and it stops working.

The problem again (and since Behe's is a biochemist he is either stupid or lying if he doesn't understand this) is that nature builds her mousetraps in a very different way.

All previous 'versions' of any particular mousetrap (or other design) HAD to work. Small changes to them, in

It seems that the subsidies in some countries, especially Germany, are keeping prices for photovoltaics panels up. Companies like Nanosolar can sell their panels for way more than manufacturing costs, because the subsidies are designed to make more conventional and expensive panels economically viable. There is a yearly degression built into the legislation, but so far it does not keep up with improvements in manufacturing.

I expect this situation to change drastically once the German market reaches saturati

In support of the parent, I'd like to point out that another challenge to adoption of each 'revolutionary' solar breakthrough is that everyone considering a massive solar project is aware that shit-piles of research funds have been rapidly re-directed towards this field. Every time some advancement is made, purchasers have to be wary that their investment won't be ridiculously obsoleted by the next advancement in a few months time. This while their investment may take years to pay itself off.

they are made from a rectangular steel frame, with engine, seats and body bolted on, so they are dead simple. Affordable? The first Ford SUV cost $40000 to make, I think, and sold for ~$60000. That, and their fuel consumtion included, tell me how is this affordable. High-tech? A crippled embedded computer, and some overpriced basic features? Jeez.

It will most likely be many years before this turns up in a product or it may not even happen at all as work on this progresses and the details are sorted out or not. It is still interesting to some people before you can buy it at Walmart or your local equivalent and you don't have to read the article if you don't want to.

There's an interesting irony to SiOnyx's business: a large chunk of the semiconductor industry's effort over the past 50 years has gone toward making silicon as pure as possible. But now SiOnyx and other companies are showing how useful--and perhaps profitable--it can be to craft silicon devices with impurities, defects, and unconventional structures.

A pure silicon crystal ingot and a doped silicon wafer are entirely different. You want a pure crystal to grow the ingot as large as possible. To make silicon useful you take the wafer sliced form the ingot, ant it has to be doped (ie add impurities) amongst many other steps.

A pure silicon crystal ingot and a doped silicon wafer are entirely different. You want a pure crystal to grow the ingot as large as possible. To make silicon useful you take the wafer sliced form the ingot, ant it has to be doped (ie add impurities) amongst many other steps.

Some impurities are introduced while growing the crystal, but most are added after the fact.

I work as an engineer in a TV station and it is painful to convince any journalist that they need to rewrite a science story. They look for pieces of information to make a compelling story. Unfortunately, they often do not have enough science background to connect the dots correctly. I understand your frustration I feel it every day. I have suggested that instead of a "science writer" they have a scientist working with a writer. Just as a positive note sometimes, they understand after I explain it to them a

Who sits around and dreams up a process like that? "Hey, I wonder what would happen hitting sulphur ions with a femtosecond laser pulse?" Just bizarre what some people sit around thinking about all day.

Sulphur Hexafluoride is commonly used in the production of silicon chips, so the only real new part here is that the sulphur was deposited using lasers. I imagine many researchers in the semiconductor industry have thought of this before.

Bizarre indeed, but on the other hand he just made a (hopefully) fantastic new from of our pal Silicaon Wafer so who are we to say anything. If you RTFA the scientist talks about the need for more people to sit around and act on their hunches rather then the immediate payoffs granted by rigid scopes. Or in other words he wants more scientists to start acting like scientists again.

Using a laser in the photo lithography process isn't to far fetched nor would seeing what happens when you start playing with high-tech toys like femtosecond laser pulses that logically go together with commonly used materials like sulfur hexafluoride which is commonly ionized into a plasma and used to etch silicon wafers.

There are already solar cells (albeit expensive ones) that are rated at 40% efficiency. Going on the low end of this how can you improve 40% by even 100X and not have perpetual motion? Heck, you think we had a Global Warming problem before, imagine how hot things are going to get once we start generating 4000% of all received solar energy.

There were two other discoveries for silicon (such as 3d structures) that claimed similar improvement. So do you get x1,000,000 improvement or only x300 improvement? Or are the improvements going to negate each other?

If you build a 3-D version of this in a pyramid shape, you could either destroy the Sun (something that Man has yearned to do since the dawn of time), take photos of the future or the past, or, if you're really ambitious, hook it up to a very powerful laser and spin it, and you could vaporize a human target from orbit.

Either way, it sounds like it's time to party with the ladies from the local cosmetology school. They're so impressive; I don't think I could handle that zero gravity stuff.

The problem with most uncooled imagers isn't insufficient sensitivity any more. It's thermal noise. Unless this improves the S/N ratio, it won't help for uncooled imagers. That's
why digital cameras which increase sensitivity in darkness show more and more noise as less
light is received.

Cooled imagers, though, as in astronomy and fancier night vision equipment, might benefit.
Cooling is done to reduce the random photons from heat within the imager. So cooled imagers
do run into the sensitivity limitations of silicon, and might benefit.

But that's an exotic application. Cooled imagers are found mostly in military, space, and astronomy. Some require liquid nitrogen. It's not a mainstream technology.

It depends. If you increase the quantum efficiency of your detector while keeping the thermal noise the same, you increase the signal to noise ratio and make a better detector.

From the articles it sounds like the black silicon has two main properties: (1) it is less reflective (that is, more photons get absorbed) and (2) electrons are easier to knock into the conduction band.

(1) should make a more sensitive detector without increasing thermal noise. (2) should make a detector that is sensitive to lower fr

If you read the journal articles http://dx.doi.org/10.1016/j.mseb.2006.10.002 [doi.org] you'll find that this process esentially creates a large number of impurity states at the center of the band gap, creating an impurity band. What this means is that light is absorbed very very fast, but then its also turned to to heat very very fast. In other words you can excite electrons but that electron will decay back down before it creates any current. This could still work for a photodetector because you can apply a voltage to sweep out the excited carriers before they recombine/decay but not for a solar cell since you want to generate power.

100-500 sounds like a lot to me, and I'm wondering how close is that to the sensitivity of the human eye's cones and rods? And are we talking about full spectrum sensors or a narrow band?
Getting anywhere close to the power of the eye would have a profound effect on the photographic world and doubly so for motion photography.

The sensors in cameras are already many many times more sensitive to light then the rods in your eyes.

Sensors exist that can detect single photons (if properly cooled). However the sensors are not as flexible as the human eye. They tend to have a linear response to light intensity rather then the eyes Log response (rods and cones don't actually respond to the intensity of light but the signal generated by a change seems to be log) although some sensors exist that produce log outputs.

The 100-500 number can't be what you think it is. The sensor in your camera is already almost good enough to detect individual photons. A factor of 2x increase in sensitivity to any given wavelength is more like it. It DOES sound like black silicon is about 2x more sensitive to visible light.

The 500x number likely comes from black silicon being sensitive to IR at lower frequencies than normal sensors are.

For your camera though, you need to have an increase in signal to thermal noise performance. Since y

Sensitivity may refer to the ratio between light and dark current. Obviously one can't knock out 500 times more electrons with the same amount of photons in this material because typical silicon photodetectors aren't THAT bad. The increase in efficiency may only be a few percent for reasons I won't go into.

I'll take your 1000 - 5000 % and at least qunituple it. There's other similarly exiciting new releases each week on solar. Within the decade we should have 25,000% efficient pannels though it could go as high as 1,000,000%. Phenomenal indeed!